About two percent of the adult population in the United States has glaucoma. Glaucoma is a group of eye diseases that causes pathological changes in the optic disk and corresponding visual field loss resulting in blindness if untreated. Intraocular pressure elevation is the major etiologic factor in all glaucomas.
In most glaucomas the source of resistance to outflow is in the trabecular meshwork. The tissue of the trabecular meshwork allows the “aqueous” to enter Schlemm's canal, which then empties into aqueous collector channels in the posterior wall of Schlemm's canal and then into aqueous veins. The “aqueous” or aqueous humor is a transparent liquid that fills the region between the cornea at the front of the eye and the lens. The aqueous humor is constantly secreted by the ciliary body around the lens, and thus there is a continuous flow of the aqueous humor from the ciliary body to the eye's front chamber. The eye's pressure is determined by a balance between the production of aqueous and its exit through the trabecular meshwork (major route) or via uveoscleral outflow (minor route). The trabecular meshwork is located between the outer rim of the iris and the internal periphery of the cornea. The portion of the trabecular meshwork adjacent to Schlemm's canal causes most of the resistance to aqueous outflow (juxtacanalicular meshwork).
Glaucoma is grossly classified into two categories: closed-angle glaucoma and open-angle glaucoma. The closed-angle glaucoma is caused by closure of the anterior angle by contact between the iris and the inner surface of the trabecular meshwork. Closure of this anatomical angle prevents normal drainage of aqueous humor from the anterior chamber of the eye. Open-angle glaucoma is any glaucoma in which the angle of the anterior chamber remains open, but the exit of aqueous through the trabecular meshwork is diminished.
All current therapies for glaucoma are directed at decreasing intraocular pressure. This is initially done by medical therapy with drops or pills that reduce the production of aqueous humor or increase the outflow of aqueous. However, these various drug therapies for glaucoma are sometimes associated with significant side effects, such as headache, blurred vision, allergic reactions, and potential interactions with other drugs. When the drug therapy fails, surgical therapy is used. Surgical therapy for open-angle glaucoma consists of laser (trabeculoplasty), trabeculectomy and aqueous shunting implants after failure of trabeculectomy or if trabeculectomy is unlikely to succeed.
Trabeculectomy is a surgical procedure used in the treatment of glaucoma to relieve intraocular pressure by creating a pathway for aqueous from the anterior chamber to the sub-conjunctival space. It is the most common glaucoma surgery performed and creates a bypass route for the aqueous humor to drain aqueous humor from within the eye to underneath the conjunctiva where it is absorbed. Additionally, glaucoma drainage devices are also frequently used for the treatment of glaucoma. These devices utilize hardware and a tube to shunt aqueous humor from within the eye to underneath the conjunctiva. Both trabeculectomy and drainage device implantation requires dissection of the external sclera and conjunctiva of the eye.
All of the currently known and performed embodiments and variations of glaucoma surgery have numerous disadvantages and moderate success rates. These modalities are currently limited by wound healing processes at the site of surgery, which are further accelerated in cases that have undergone previous conjunctival or scleral surgery. The wound healing and scarring process associated with glaucoma surgery involving the conjunctiva and sclera also limits the ability to perform subsequent glaucoma surgery in the same location. Therefore, there is a great clinical need for the treatment of glaucoma by a method that would be faster, safer and less expensive than currently available modalities, which involve either substantial trauma to the eye and require great surgical skill by creating a hole over the full thickness of the sclera or cornea-scleral junction to create a flow path from the anterior chamber into the subconjunctival space or by placing a permanent device into the eye.
The morbidity associated with trabeculectomy consists of failure (10-15% per year), infection (a lifelong risk about 2-5%), choroidal hemorrhage (1%, a severe internal hemorrhage from pressure too low resulting in visual loss), cataract formation, and hypotony maculopathy (potential visual loss from pressure too low).
Thus, it would be desirable to develop a surgical system and method for treating glaucoma that does not require a conjunctival and scleral incision, which in turn would hasten patient healing and improve recovery time. Such a procedure would also spare the sclera and conjunctival tissues, allowing ab-externo surgery at a later date if needed.